fix: revert vite-plugin-svelte 7.0.0 -> 5.1.1 (requires vite 8)

Dependabot PR #189 bumped to 7.0.0 which requires vite ^8.0.0 but
we're on vite 6.4.1. Revert to 5.1.1 which is compatible.

cc

package.json

@@ -36,7 +36,7 @@
   "devDependencies": {
     "@sveltejs/adapter-static": "^3.0.6",
     "@sveltejs/kit": "^2.52.2",
-    "@sveltejs/vite-plugin-svelte": "^7.0.0",
+    "@sveltejs/vite-plugin-svelte": "^5.1.1",
     "@tauri-apps/cli": "^2",
     "@testing-library/svelte": "^5.3.1",
     "jsdom": "^27.4.0",